LeetCode 108. Convert Sorted Array to Binary Search Tree

题目描述

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.
For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

Example:

Given the sorted array: [-10,-3,0,5,9],

One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:

      0
     / \
   -3   9
   /   /
 -10  5

题目思路

代码 C++

• 思路一、二分查找的方法构建二叉平衡树

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* sortedArrayToBST(vector& nums) {
        if(nums.size() == 0){
            return NULL;
        }
        return core(nums, 0, nums.size()-1);
    }
    
    TreeNode* core(vector& nums, int left, int right) {
        if(left <= right){
            int indexOfmed = (left + right) / 2;
            TreeNode* root = new TreeNode(nums[indexOfmed]);
            root->left  = core(nums, left, indexOfmed-1);
            root->right = core(nums, indexOfmed+1, right);
            return root;
        }
        else{
            return NULL;
        }
    }
};

总结展望